Cooking for yourself definitely saves time. Are you counting travel time and time spent waiting in line? But it does take slightly more effort, and require the right tools.
You can always stick to the basics. Ramen takes ~10 minutes for boiling water and clean up. Chicken breast takes 2 minutes to season, 14 minutes to cook and clean. Tuna takes no effort right out of the can. Boil or steam vegetables for about 5 to 10 minutes. Rice or oatmeal are cheap sources for carbs.
With these ingredients, you can eat well for under $10 / day where I live (Providence, RI). Just make sure you invest in a good spice rack.
And it's worth noting that cooking for yourself doesn't always save time. After you consider preparation and cleanup, sometimes it consumes more.
It can also be stressful if you don't have a nice kitchen, or if you have to share your kitchen with others. Although probably one of the benefits of having founders living together is optimizing your kitchen.